The invention relates to improvements in the field of drug delivery. More particularly, the invention relates to polypeptides, conjugates and pharmaceutical compositions including the polypeptides of the invention and their use for transporting agents (e.g., therapeutic agents) across into particular cell types such as liver, lung, or kidney.
Diseases of the liver, including hepatitis (e.g., viral hepatitis) and cancers of the liver (e.g., hepatocarcinoma), and lung diseases, such as lung cancer (e.g., small cell and non-small cell lung cancer) are serious health problems. Many therapeutic agents for such diseases have undesirable side effects (e.g., chemotherapeutic agents) or, for reasons such as in vivo stability, transport, or other pharmacokinetic properties, are difficult to provide at a sufficiently high concentration in the target tissue or for a sufficiently long duration to allow maximal therapeutic effect in the target tissue.
Accordingly, there is a need for methods and compositions that increase concentrations of therapeutic and diagnostic agents in target organs or tissues.